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February 19, 2010

Winter bee loss? Why and what's the answer?

Fig. 1
Every year we beekeepers wonder why our bees die over the winter.  This last winter it looks like we are approaching 50% losses. After over 150+ years of beekeeping, is there still some part of this equation we don't understand?  Is it simply that we fail to see the answer or is it that each generation of beekeepers just does not know about beekeeping's past?

This is the normal scenario we hear:
"I went to check on my hives because we had a warm day and found that _?_ number of my hives had died out.  I looked inside and there was a large amount of bees in the bottom of the hive.  I found a small cluster of dead bees in must have been the nucleus.  I'm not sure why they died.  They were off to one side of the hive and not in the middle of the hive like you see in the textbooks.  There was plenty of honey nearby, my friend beekeeper told me to move frames of honey in the hives so the bees had honey above them and beside them.  Do you think this is caused by some new virus?  Do you have any idea why my bees died?"

Fig. 2 Infrared of hives
Any good mystery starts with a gathering of facts.  In the above scenario there was not enough information presented to help find the answer.  But nevertheless, this is what even the experts give as examples. Let's put our thinking caps on, coupled with an open mind and salted with a little history and we should be able to crack this mystery. To understand what happened we need to know and acknowledge:
  1. Some generally accepted scientific information about bees, bee pests and bee diseases
  2. Some beekeeping history
  3. Some thermal information
  4. How we as beekeepers manage and care for our hives and our bees
  5. and some basic common sense
Fig. 3 
Other considerations are:
  • Type of hive used
  • Orientation of hives
  • Insulation
  • Ventilation
  • Foods given or stored to/by the bees
  • Keeping hives warm or cold
  • Strength of hive
Bees are effected by the temperature of the air. Bees move away from cold areas of the hive seeking the warmest parts of the hive (see fig 2.) Generally, bees start to cluster at about 57°F.  At about 45°F they become immobile.  Their body temperature can be higher than this allowing them to move about the cluster or change positions in the cluster.  One common falsehood is thinking the bees heat the inside of the hive.  They do not.  There goal is to heat the cluster.
    As the cluster is formed other pests cluster with it.  SHB's can form their own clusters within the bee cluster.  A smaller number of SHB's will just coexist with the bee cluster.  The impact of these overwintering SHB's is that they eat some of the eggs from the queen as soon as the are layed.  Thus you have less bees for wintering and spring.  Varrora will also overwinter with the bees.  Diseases will also take a toll.

    Over the many years of beekeeping there have been many different approaches to wintering bees. Early years saw the bees in special structures or placement into basements.  Later years saw the introduction of outside wintering of hives, double wall hives and wrapping/insulating of hives.  There was a general acceptance that bees needed protection of some sort from the cold. However there was no agreement of how best this was to be done.

    Looking at Fig.2, you can see that the standard hive is a thermal nightmare, leaking the heat generated by the bees inside.  While this has value during summer, it offers little protection for the bees in winter.  Bees will shift the cluster away from the coldest wall (s) of the hive and airleaks such as in Fig.3. This is usually why the cluster is off center during winter.

    As beekeepers focused on profits, standardization and easy of use of hives, the bees were looked at more like cattle.  They were plentiful and healthy without the threats of today. Management practices were geared for the beekeeper.  Today, proper treatments for pest/disease controls must be in place before wintering and timely work must be performed by the beekeeper.

    More bees are lost to starvation than anything else.  In fig. 1 the bees are dead first from starvation and second from cold.  The bees on the top of the comb were the "outer shell" of the cluster, keeping the inner bees warm.  These can be seen head in comb tail out.  Without the inner heat from the cluster and no food they were doomed.

    In the next section "Wintering Honey Bees" we will cover what to do and what not to do regarding wintering bees.  We will also go over a general plan of action for your bees including preparing for the spring.  I hope to have it up soon.

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